1. Technical Field
The present invention is related to an airflow control apparatus for an environmental control system. More particularly, the present invention is related to an adaptive control system for positioning damper systems or controlling air units utilized in an environment control system.
2. Discussion
Environment control networks, facility management systems, and damper systems are employed in office buildings, manufacturing facilities, and appliances for controlling the internal environment of the facility. For example, in a heating, ventilating, and air conditioning (HVAC) system, controlled air units (e.g., variable air volume (VAV) boxes, unitary devices (UNT) or damper systems) are located throughout the facility and provide environmentally controlled air to the internal environment of the facility. The controlled air is provided at a particular temperature or humidity so that a comfortable internal environment is established. The air flow rate of the controlled air is preferably measured in cubic feet per minute (CFM).
The VAV boxes are coupled to an air source which supplies the controlled air to the VAV box via duct work. VAV boxes and unitary devices provide the controlled air through a damper. The damper regulates the amount of the controlled air provided to the internal environment. The damper is coupled to an actuator which preferably positions the damper so that appropriate air flow (in CFM) is provided to the internal environment.
A controller is generally associated with at least one actuator and damper. The controller receives information related to the air flow and temperature in the internal environment and appropriately positions the actuator so that the appropriate air flow is provided to the internal environment. The controller may include sophisticated feedback mechanisms such as proportional integral (PI) control algorithms. Sophisticated feedback mechanisms allow the actuator to be positioned more precisely.
More particularly, the controller generally includes a flow control system for positioning the actuator so that the damper provides a desired amount of air flow. The flow control system typically measures the actual air flow across the damper and adjusts the position of the actuator until the desired amount of air flow is provided by the controlled air unit. In such systems, the performance of the flow control system (e.g., the accuracy or precision of the position of the system damper) is critical to reliability, energy efficiency, and overall performance of the HVAC system and controlled air unit. Poor flow control often leads to degraded temperature control performance, decreased efficiency for the controlled air unit, and premature mechanical failures for the actuator and damper system associated with the unit.
Heretofore, flow controllers or flow control systems in HVAC systems are prone to slow response and poor disturbance rejection due to the inherent non-linear behavior and measurement noise associated with controlled air units such as VAV boxes. The measurement of actual air flow is strongly affected by turbulence. Additionally, friction, hysteresis, and non-linear relationships between the flow rate and damper position complicate the control of damper systems. A traditional approach to solving these problems involves the use of proportional, (P), proportional-integral (PI), or proportional-integral-derivative (PID) positioning algorithms for the damper.
Thus, there is a need for a flow controller which is less prone to sluggishness and oscillatory behavior. There is also a need for a flow controller which can be set to have a low duty cycle and yet provide acceptable setpoint tracking. Finally, it is desirable to provide a flow controller that can quickly switch back and forth between two or more operating modes which adaptively control the setpoint tracking performance.